The Magnetic And Transport Properties Of Ru-doped Manganites

Many interesting physical properties are observed in manganites, such as colossal magnetoresistance (CMR), colossal electroresistance (CER), isotope effect and multiferroic etc. The researches on manganites are thorough and extebsive nowadays, Electronic phase separation (EPS) in manganites has triggered considerable interest in scientific studies due to their exotic electrical and magnetic properties, The EPS refers to the coexistence of multiple electronic phase including ferromagnetic metallic (FMM) and antiferromagnetic charge-ordered insulating (AFM/COI) phase, which are the results of the strong competing interactions between charge, spin, orbital, and lattice degrees of freedom.The phase competition varies sensitively with the small value of ionic or electronic doping at Mn-site, which provides insight into the natures of EPS. It is found that a slight Ru substitution for Mn ions in many manganites favors the formation of FMM states and the raise of Curie temperature, which is very different from the other ionic substitutions (e.g., Cr, Fe and Al) and thus has received mush special attentions. Previous investigations indicate that the doped Ru ions in manganites are mainly Ru4+with a small fraction of Ru5+, and argue that the raise of Curie temperature contributes to the ferromagnetic (FM) superexchange interaction between Mn3+and Ru4+(Ru5+), However, the exact Mn-O-Ru interaction and its effect on EPS are still in debate. Furthermore, the understanding on the unusual metal-insulator transition (MIT) induced by the Ru-doping is still unclear. We investigate the magnetic and transport properties of polycrystalline bulk Lao.225Pro.4Cao.375Mn1-xRuxO3 (x□0.15) in this thesis. The main contents are highlighted as follows:In chapter 1, an overview of manganites and the presentation of main physical properties on manganites are given, followed by the description on colossal electroresistance (CER).In chapter 2, the preparation method and characterization methods of the samples are given in this part. Then we briefly introduce the experimental apparatus for testing samples in PLD laboratory and the principle of them.In chapter 3, polycrystalline La0.225Pr0.4Cao.375Mn1-xRux03 (x=0,0.01,0.02,0.03,0.05, 0.07,0.1, and 0.15) samples were syn-thesized by the standard solid-state-reaction method. We investigate the magnetic and transport behaviors of the Lao.225Pro.4Cao.375Mn1-xRux03 (LPCMRO)。We tested the temperature dependent magnetization and the temperature dependent resistivity of LPCMRO (x=0,0.01,0.02,0.03,0.05,0.07,0.1, and 0.15). Besides, an abnormal electroresistance effect, i.e., the resistivity increases with the electric field, is observed in LPCMRO. The magnetic field induced suppression of such abnormal electroresistance effect is also observed. These interesting physical phenomena are analyzed and discussed in this section.In chapter 4, the conclusion of this thesis is made and perspectives based on it are highlighted.